There are many electrical devices which emit high energy electrons from a heated cathode for transport along an electrical field to an anode. In some devices a low pressure gas as included between the cathode and the anode for interaction with the emitted electrons. In one mode of interaction the electrons collide with the gas molecules and when enough energy is delivered in a collision the gas molecule may be ionized to also generate another electron. Thus, the initial emitted electrons may produce a cascading ionization to transmit substantial power through the device.
The highly ionized gas resulting from the collisions is called herein a "plasma" and the electrical charge flow associated with movement of the plasma constitutes current flow. Once a plasma condition is initiated it is relatively self-sustaining until the electron flow is interrupted or until the plasma is cooled below the energy levels necessary for ionization.
A conventional device using the high power capability of a plasma flow is a thyratron. A control grid is provided between the cathode and the anode for accelerating the emitted electrons from the cathode to an energy adequate to initiate the cascading ionization. Thereafter, voltage on the control grid may be removed with no effect on the plasma flow. Conventional attempts to terminate the plasma flow are slow-acting, require large amounts of energy, and frequently affect a substantial portion of the plasma volume such that reformation of the plasma does not readily occur.
Conventionally, the switching, or quenching, of the plasma uses external coils for affecting the net electromagnetic field within the device. A coil which produces the required magnetic field typically has a large inductance from the external coil size needed to affect the interior volume. High frequency operation is not practical with such large volume external coils.
In a prior art device described in U.S. Pat. No. 4,071,801 to Harvey, a concentric electrode device is described where an axial magnetic field accelerates electrons in a spiral annular path between the electrodes to generate the cascading ionization. An off-switching magnetic field coil is provided at an off-axis location to generate a magnetic field in a relatively small portion of the annular volume. A tangentially oriented magnetic field is produced which affects the electron path to intersect with the anode and remove electrons. As taught by the reference, the auxiliary field coil produces an off-axis perturbation in the main magnetic field such that sufficient electrons are eventually removed from the volume to switch off the plasma.
Thus, one object of the present invention is rapid quenching of a plasma flow.
Another object of the present invention is to provide for pulse-type response in a device having ionized gas flow.
Still another object is to control a hot gas device.
One other object of the present invention is to maintain significant volumes of the gas in a state conducive to rapid reinitiation of plasma flow after quenching.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.